Compression refrigerating system utilizing a free-piston compressor



Aprll 12, 1960 SCHLUMBQHM 2,932,172 COMPRESSION REFRIGERATING SYSTEM UTILIZING A FREE-PISTON COMPRESSOR Filed Aug. 20, 1958 .116 7 Fig.2

U ited States. aten T Q7 COMPRESSION REFRIGERATING SYSTEM UTI- LIZING A FREE-PISTON COMPRESSOR v PeterSchlumbohm, New York, NY.

Application August 20, 1958, Serial No. 756,254 3 Claims. '(Cl. eta-7 The present invention refers to a refrigerating system of the type in which a liquid refrigerant is evaporated to producecold and in which thevapors are compressed into the liquid phase for reevaporation. More specifically it refers to a refrigerating system in which the compression of the refrigerant vapor is performed by a freepiston compressor. A refrigerating apparatus of that type has been used with natural gas as fuel in a combustion space and with Freon vapors being compressed by the piston in a compression space of a conventional closed Freon compression cycle.

Inasmuch as the free-piston oscillates in such a case between the combustion space of the fuel and the compression space of the refrigerant vapor, the main trouble has been to seal those two spaces against each other. This problem has not yet been solved; a leakage through the space around the body of the piston seems to be unavoidable. Such leakage, due to the varying pressures in the two spaces, occurs both ways. Leakage of Freon refrigerant from the compressing space into the combustion space means loss of refrigerant and interference with the combustion. Leakage of natural gas or the products of its combustion, such as carbon dioxide, from the combustion space to the refrigerant compression space means accumulation of non-condensible gases in the condenser of the Freon cycle and lowers the efficiency of the refrigerant cycle considerably.

Following my invention, I am utilizing the same chemical substance as fuel on the one side of the free-piston and as refrigerant on the other side of the free-piston. By this method I solve the'pro'blem of leakage through the space around the body of the piston from the compression space to the combustion chamber. Inasmuch as the same chemical substance is leaking through, this substance becomes fuel in the fuel combustion chamber.

By an additional method step, I take care of leakage from the combustion chamber through the space around the body of the piston into the refrigerant compression space. I am constantly purging the compression space and I am feeding the vapors and gases which leave through this purging line, into the fuel intake of the combustion space. Again, due to the chemical identity of the refrigerant and the fuel, such refrigerant becomes fuel.

The method can be executed with chemical substances which are suitable for the dual purpose of refrigerant and fuel. There are two outstanding substances-propane and butane-which are suitable for this method. Of these, Propane is the more ideal one.

The invention is illustrated diagrammatically in Fig. 1 of the accompanying drawings. Fig. 2 shows a structural detail. In Fig. 1 the oscillating free-piston 20 is shown diagrammatically in its position between the propane refrigerant compression space 19 and the propane fuel combustion chamber 21. The propane refrigerating vapors leave the compression space 19 through a pipe 22 which leads into the condenser 23. From the condenser 23 2,932,172 w ned p 2. 1 96 the liquifiecl propane flows into the receiver tank'24 which is shown partly in view and partly in a vertical section. From the receiver tank 24 the liquid refrigerantflows through an expansion valve 16 into the evaporator 15. A second line 18 connects the evaporator 15 with the compression space 19.

The cycling of the refrigerant is not unlimited but limited. Part of the refrigerant which is filling the space of the condenser 23 is leaving through a branch tube 25 and a purging line 26 and pressure reduction valve 27 to flow into the fuel combustion space 21. yThis means that the level of the refrigerant in the receiver 24 would go down unless new refrigerant is fed into the compremsion system. As shown in Fig. 1, at a certain level point 28 of the receiver, a tube 29 branches off which leads into a secondary evaporator 9. 'If liquid is present at the level point 28, liquid refrigerant will enter the secondary evaporator 9 and will evaporate there when leava ing a capillary nozzle 10. The cold produced in this secondary evaporator 9 will in that moment cool the thermal bulb 8 of a fill-up valve 7. The fill-up valve 7 is connected with an intake line 5 to the space of a fuel tank 1 which is shown in a side view, partly in view and partly broken away, and whose lower space is filled with liquid fuel-refrigerant, and whose upper space is filled with the vapors of the liquid.

The shut-off valve 4 and a solenoid valve 6 allow to shut-oif this line 5. The valve 7 has an outlet tube 12 which is connected to the space of the evaporator 15. A simple cross arrangement 11, shown in detail in Fig. 2, illustrates how the intake .14 of the evaporator 15 is connected to the outlet 12 of the control valve 7, to the outlet 13 of the control valve 16, through which liquid refrigerant enters into the evaporator, and finally to the outlet 30 of the secondary evaporator 9.

The control valve 16 is a conventional expansion valve controlled by the thermal bulb 17 and it is the same type as the control valve 7 with its thermal bulb 8. Such valves open when the temperature of the thermal bulb is raised and close when the temperature of the thermal bulb is going down.

The arrangement shown works as a control of the level of the refrigerant at the level point 28. As stated above, when there is liquid at this level point the thermal bulb 8 of the control valve 7 will be cooled and the valve 7 will be closed. If there is no liquid at the level point 28, hot condenser vapor will enter throughtube 29 into the secondary evaporator 9. This will warm the thermal bulb 8 and this in turn will open the control valve 7. When this valve 7 is open, vapor 3 from the tank 1 will flow through tubes 12, 11 and 14 into the evaporator 15 and into the suction line 18. This newly entered vapor will then be compressed and condensed and will raise the liquid level in the receiver 24. When this level is raised to the level point 28 or above, liquid will enter through tube 29 into the secondary evaporator 9. The cold here produced will cool the bulb 8 and close the fill-up valve 7.

Inasmuch as the purging line 26 provides the fuel for the combustion space 21, the purging involves a considerable volume of vapor and thus this arrangement is very well suited to solve the leakage around the piston 20 when such leakage, combined with difiusion, occurs in the direction from the combustion space 21 towards the compression space 19.

On the other hand, a leakage around piston 21 in the direction from the compression space 19 to the combustion space 21 is without any bad effects on the combustion process as the vapors originating from compression space 19 are actually the same fuel vapors which enter 1tihf gosmbustion space 21 through the purging-and-fuel 'Having eliminated the bad consequences of leakage around piston 20, one can be much more lenient concerning the sealing means around the piston 20. One may even resort to sealing means which are based on the effect of capillary dimensions of a free space between the body of the piston 20 and the surrounding piston chamber and which do not require mechanical contact between them.

Generally speaking, in a compression refrigeration cycle which applies the free-piston as compressor piston, this new method improves the operation of the fuel combustion and the operation of refrigeration compression, even with conventional sealing means applied to the piston. Moreover, by counteracting the leakage, the new method of operation reduces the damage of leakage and opens the way to afree-pis'ton with reduced mechanical sealing means and increased efiiciency.

I claim as my invention:

- l. Compressiomrefrigerating system utilizing a freepiston compressor and a refrigerant which is suitable as motor fuel; comprising an'evaporating, compressing and condensing circuit having an evaporator, a suction line, a compression line, a condenser, a receiver, a purging line, and a free-piston compressor; said free-piston compressor comprising a combustion space on one side of the free-piston and a refrigerant-compressing space on the other side of said piston; said suction line connecting said evaporator with said refrigerant-compressing space and said condensing line connecting said refrigerant-compressing space with said condenser; said purging line connecting said condenser with said combustion space; whereby leakage of fuel or combustion gases from said combustion space via the piston surface into said compression space may leave the condenser space through said purging line and, mixed with refrigerant vapor, return into the combustion space; and whereby leakage of refrigerant from said refrigerant-compression space via the piston surface into said combustion space may be used as fuel.

2. In the apparatus as claimed in claim 1, the use of propane as refrigerant-fuel.

References Cited in the file of this patent UNITED STATES PATENTS 2,844,301 Newton July 23, 1958 

